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Isolation, Screening and Application of Nitrite-Degrading Lactic Acid Bacteria from Salted Fish

Author: LiuFaJia
Tutor: WuYanYan
School: Guangdong Ocean University
Course: Aquatic Products Processing and Storage Engineering
Keywords: Salted fish Lactic acid bacteria Degradation of nitrite Isolation andscreening Application
CLC: TS254.1
Type: Master's thesis
Year: 2012
Downloads: 150
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Abstract

Salted fish is a tradition characteristic preserved aquatic product, an important partand a typical representative pickled product of China. It has a nutrient-rich, rich flavor,ease of storage, and consumption of convenient features.Salted fish has a vast consumermarket and a long history of processing and consumption of coastal areas in China andSoutheast Asia. However, epidemiological investigation showed that in coastal areas,regular consumption of preserved aquatic populations the incidence of gastric cancerhigher, it is closely related to the high nitrite content of preserved aquatic products.Therefore, how to ensure that the food security of the traditional salted fish and otheraquatic food and better circulation in the domestic market, is one of the urgent problemsof current marinated seafood processing industry. Lactic acid bacteria have degradationcharacteristics of nitrite, optimizing the good lactic acid bacteria with efficientdegradation of nitrite, and used into practice, has high feasibility and significance. Thispaper as a starting point to natural selection, Isolation and screening of lactic acidbacteria with nitrite degradation ability from traditional salted fish：Lactobacillusplantarum and Pediococcus pentosaceus. Studied the biological characteristics andfactors affected nitrite degradation of the two strains. Determined the optimum conditionof degradation conditions， and applied in the production practice of salted fish.Comparision the differences of microbiological index, physical and chemical index,security index and sense index between the lactobacillus method and the traditionalmethod in salted fish processing.The main research contents and conclusions are as follows:1. Twelve lactic acid bacterias with nitrite degrading ability were isolated from thetraditional salted fish. Nitrite degradation ability of the12strains had a comparativeanalysis in MRS broth, optimized three degradation of nitrite higher strains b2, j2, and j5.b2in the72h later the degradation rate of nitrite was96.2%, j5nitrite degradation rate was91.2%, j2nitrite degradation rate was85.6%. According to their physiological andbiochemical characteristics and phylogenetic analysis based on the16S rDNA sequence,b2was Lactobacillus plantarum, j2was Leuconostoc mesenteroides and j5wasPediococcus pentosaceus.2. Studied the biological characteristics of lactic acid bacteria. The optimumtemperature: lactic acid bacteria had a wider temperature range, the optimum growthtemperature range of20℃⁴0℃, but Pp had strong temperature tolerance, with goodgrowth status at45℃. Salt tolerance: three lactic acid bacteria in NaCl concentrationrange of0to10%, Lp and Pp had strong tolerance to NaCl, when the NaCl concentrationof5%to10%, there was not much affected to their grow; The NaCl tolerance of Lm isrelatively weak, when the NaCl concentration within5%¹5%of its growth wasplummeting; when the NaCl concentration reached or exceeded20%, the three bacteriabasically had no growth signs..3. Lactic acid bacteria to the degradation of nitrite factors: temperature, pH is verysensitive to the three lactic acid bacteria degradation of nitrite. Optimum t degradationemperature was about35℃, optimum degradation pH was5.5; The three lactic acidbacteria had good tolerance to the NaCl, especially below10%the degradation of nitritewere quite obvious. There was no action of antagonism between Lp and Pp， Lm andPp，so they could be used as a mixed fermentation Test.4. Lactobacillus plantarum and Pediococcus pentosaceus isolated and identifiedfrom the traditional salted fish used in salted fish，and the degradation conditions wereoptimized. The optimum conditions were: the ratio of Lp: Pp is2:1, fermentationtemperature was30℃, fermentation time of20h. Under this condition, the salted fishhad low nitrite content with excellent quality, flavor and taste. Verification tests carriedout according to the optimum conditions, it showed that the sensory score of86.86points,nitrite content was0.48mg·kg^-1in salted fish.5. The research on lactic acid bacteria method for processing salted fish qualitycharacteristics: lactic acid bacteria method for processing salted fish products in thephysicochemical and microbiological indicators of traditional methods of processingsalted fish products are not significant differences. Method for processing salted fish inlactic acid bacteria in the appearance, taste, taste and other sensory score and the contentof volatile flavor compounds better than the traditional method of processing salted fish products; nitrites, nitrosamines, biogenic amine content are much lower than traditionalmethods processing salted fish.

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